This invention relates to a process of producing a diesel fuel/water emulsion for the operation of diesel engines which, in addition to a reduction of soot formation and more favorable exhaust gas emission values (less NO.sub.x), results in an interior cooling of the engine and thus in lower exhaust gas temperatures with improved efficiency. In this case, it was found that it is most advantageous for the engine to be operated by varying the water content in the fuel as a function of engine parameters, such as load, speed, engine temperature, etc., rather than using a constant fuel/water ratio.
A process is shown in German Patent DE-OS No. 32 37 305 in which an injection arrangement is described. In this arrangement, separate injection system is provided that has its own injection pump for the water to be admixed, in addition to the actual diesel fuel injection system. The former system leads into the diesel fuel injection system between the diesel fuel injection pump and the pertaining injection valve. For the proportioning of the water quantity to be admixed, an electronic control system is provided that takes into account the exhaust gas temperature, the fuel consumption and/or the speed. The disadvantage in the case of this system is mainly that for the admixing of the water, an additional expensive high-pressure injection pump must be provided. A further disadvantage is that water and diesel fuel are brought in contact with one another in the high-pressure part of the injection system, which does not result in an especially intimate mixing of water and fuel. However, an especially fine and intimate mixing of water and fuel is especially advantageous for the combustion process.
An object of this invention is to improve the initially described admixing proces to the extent that an improved mixing of the fuel and the water is achieved. A further object of the invention is to provide a fuel/water mixing process which requires only one injection pump.
The objects of the present invention are achieved by providing a process of producing a diesel fuel/water emulsion for a diesel engine which includes supplying quantities of water and diesel fuel separately to the intake side of an injection pump. The quantities of diesel fuel and water are then mixed in a cylinder of the injection pump. By means of the intake stroke of the injection pump, an especially good mixing and swirling-together of diesel fuel and water will take place.
According to another advantageous embodiment of the invention, an emulsifying agent may be added to the diesel fuel or the water in a way that is known per se. The emulsifying agent supports the formation of the emulsion and contributes to the stabilizing of the formed emulsion. Factors determining whether and in what amount such an addition of the emulsifying agent is necessary include the size of the engine, the quality of the diesel fuel used, the length of the lines from the injection pump to the injection nozzle, etc. The advantages of the addition of an emulsifying agent in an individual case should be determined by experimentation.
It is known that diesel injection pumps operate with a constant piston stroke. In previous injection pumps, the part of the displacement not required, i.e., the excess amount of fuel in the case of conventional diesel engines, is returned into the fuel system in front of the pump.
According to another advantageous embodiment of the invention, this conventional return does not take place, and the excess amount of fuel is stored temporarily in an accumulator and is then added to the injection pump during the next intake stroke.
In an advantageous embodiment of the invention, the accumulator is preferably operated at a pressure that is higher than the pressure in the water and diesel fuel feeding systems following pumping, but lower than the pressure that is required for the opening of the pump check valve on the high-pressure side or of the injection nozzle valve. In this way, the emulsion stored in the accumulator is preferably taken into the injection pump cylinder during the intake stroke. Furthermore, during the intake stroke, fuel is prevented from flowing from the accumulator, past check valve 3 into the engine which would be noticed at the injection nozzle as "after-dripping".
The production of different amounts of water and diesel fuel can take place in many ways. However, it is preferable to keep the fuel and the water in the lines leading to the injection pump under constant pressure and to adjust the quantitative proportion of water to fuel by means of controlled screen openings (control valves). Another very simple, and therefore also preferred, solution is to produce the quantitative proportions by means of timed flow valves. In these cases, the quantity control is a result of the ratio of the times in which the valve is opened or closed.
The different quantities of water and diesel fuel are led separately to the intake side of the injection pump. In this case, it is possible to equip the injection pump with two intake openings for water and diesel fuel. It is also possible to use only one intake opening and to lead the fuel and the water flow together directly in front of this opening. By means of the swirling-together during the intake stroke, a very good formation of the emulsion is obtained. The water part in the injected mixture may be between 0 (cold start) and up to about 30 percent by volume. The quantitative proportions, that are adjusted by a conventional electronic control system by means of engine operating parameters, depend on the purpose that is to be achieved with the admixture of water. These purposes include, for example, saving as much diesel fuel as possible, achieving the most favorable exhaust gas emission values, or maintaining the highest possible engine performance. These parameters must be determined by the constructor of the engine by means of his technical knowledge.